#include "postgres.h"

#include "fmgr.h"
#include "catalog/namespace.h"
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "utils/builtins.h"
#include "utils/guc.h"


PG_MODULE_MAGIC;

void		_PG_init(void);
void		_PG_fini(void);

static char *ignore_index = NULL;

static void my_get_relation_info(PlannerInfo *root, Oid relationObjectId,
								 bool inhparent, RelOptInfo *rel);


/*
 * Get control during planner's get_relation_info() function, which sets up
 * a RelOptInfo struct based on the system catalog contents.  We can modify
 * the struct contents to cause the planner to work with a hypothetical
 * situation rather than what's actually in the catalogs.
 *
 * This simplistic example just removes any index that matches ignore_index
 * by name.
 */
static void
my_get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
					 RelOptInfo *rel)
{
	RangeVar   *relrv;
	Oid			indexoid;
	ListCell   *ilist;
	ListCell   *prev;

	/* Do nothing unless ignore_index has been set */
	if (ignore_index == NULL || *ignore_index == '\0')
		return;

	/*
	 * Look up the index.  No complaint if not found.
	 *
	 * Note: doing this lookup again each time is a bit inefficient, but
	 * for the contexts in which this plugin would be used, it probably
	 * isn't worth making this faster.
	 */
	relrv = makeRangeVarFromNameList(stringToQualifiedNameList(ignore_index));
	indexoid = RangeVarGetRelid(relrv, true);
	if (!OidIsValid(indexoid))
		return;

	/* If it's in the rel's list of indexes, delete it */
	prev = NULL;
	foreach(ilist, rel->indexlist)
	{
		IndexOptInfo *ind = (IndexOptInfo *) lfirst(ilist);

		if (ind->indexoid == indexoid)
		{
			rel->indexlist = list_delete_cell(rel->indexlist, ilist, prev);
			break;				/* can't be more than 1 match */
		}
		prev = ilist;
	}
}


/*
 * _pg_init()			- library load-time initialization
 *
 * DO NOT make this static nor change its name!
 */
void
_PG_init(void)
{
	/* Get into the hooks we need to be in all the time */
	get_relation_info_hook = my_get_relation_info;
	/* Make ignore_index accessible through GUC */
	DefineCustomStringVariable("ignore_index",
							   "Name of an index to ignore",
							   "",
							   &ignore_index,
							   PGC_USERSET,
							   NULL,
							   NULL);
}


/*
 * _PG_fini()			- library unload-time finalization
 *
 * DO NOT make this static nor change its name!
 */
void
_PG_fini(void)
{
	/* Get out of all the hooks (just to be sure) */
	get_relation_info_hook = NULL;
}